Cancer is a major cause of death and was responsible for approximately 7.6 million deaths worldwide (around 13% of all deaths) in 2008 according to the World Health Organization. Although notable successes have been achieved in the pharmacological therapy of a number of tumor types, many tumors remain difficult to treat. For example, the median life expectancy of people with glioblastoma multiforme (GBM), the most common primary brain tumor in adults, is about 12-18 months post-diagnosis, even when treated with current state of the art therapies. There is a need for new targets and therapeutic approaches for the treatment of cancer.